Piston Compressor Having a Venting Device

ABSTRACT

A piston compressor is provided for compressing a gas, which optionally can be disconnected from a drive device by way of a clutch. The piston compressor has an inlet valve, which is arranged between an inlet line for gas to be compressed and a compression chamber of the piston compressor, and an outlet valve, which is arranged between the compression chamber of the piston compressor and an outlet line for compressed gas. The piston compressor has a venting device, by which compressed gas can be led out of the compression chamber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No. PCT/EP2017/051406, filed Jan. 24, 2017, which claims priority under 35 U.S.C. § 119 from German Patent Application No. 10 2016 201 208.8, filed Jan. 27, 2016, the entire disclosures of which are herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a piston compressor for compressing a gas, which is optionally separable from a drive device by means of a clutch, having an inlet valve, which is arranged between an inlet line for gas to be compressed and a compression chamber of the piston compressor, and an outlet valve, which is arranged between the compression chamber of the piston compressor and an outlet line for compressed gas.

Compressors of this type are used for example for the compressed-air supply of commercial vehicles, in particular for the compressed-air supply of the brake system. In this case, the compressor is driven via the drive train of the combustion engine. Applications are known in which a clutch is arranged between the compressor and the drive connection in order to separate the compressor from the drive when the compressed-air system of the commercial vehicle is filled with compressed air. In known embodiments, at the same time as the clutch is opened, the outlet line of the compressor is emptied. When the compressor is restarted, the pressure in the then pressure-free outlet line has to be built up again before compressed air can be delivered into the compressed-air system. In order to avoid such efficiency losses, solutions are also known in which the outlet line is not switched into a pressure-free state while the piston compressor is not being driven.

In piston compressors of the abovementioned type, there is the risk of an outlet valve developing a leak as a result of contaminants such as deposits caused by residues of lubricating oil or in particular particles detached by such residues. In this case, the outlet valves frequently have a valve tongue, between which and the valve seat thereof such contaminants can pass and prevent the valve from closing fully there. In the case of an outlet-valve leak, resulting for example therefrom, in conjunction with a pressurized outlet line during the separation of the compressor from the drive, compressed air can pass back into the compression chamber of the compressor. The pressure in the compression chamber of a piston compressor in a 12.5-bar system can then rise to up to 6 bar. When the piston compressor is restarted with such a high pressure in the compression chamber, during the first compression stroke of the piston, the gas in the compression chamber is compressed to about 60 bar. The resultant torque is much too high for the clutch, which in this case slips, overheats and wears inadmissibly heavily. In addition, such a high pressure in the compression chamber can also result in damage to the compressor itself.

Therefore, the invention is based on the object of providing an improved piston compressor which avoids the abovementioned drawbacks and the resultant undesired effects.

In order to achieve the object, a piston compressor for compressing a gas is provided, which is optionally separable from a drive device by way of a clutch, having an inlet valve, which is arranged between an inlet line for gas to be compressed and a compression chamber of the piston compressor, and an outlet valve, which is arranged between the compression chamber of the piston compressor and an outlet line for compressed gas. The piston compressor has a venting device, through which compressed gas, which passes from the outlet line back into the compression chamber during the separation of the piston compressor from the drive device, is able to be discharged from the compression chamber.

Such a piston compressor has an inlet line, which is in particular part of an inlet system and through which a gas to be compressed is conveyed to a compression chamber of the piston compressor. In this case, an inlet valve is arranged between the inlet line and the compression chamber, said inlet valve being open while gas to be compressed is being drawn into the compression chamber (the pressure in the compression chamber is lower than the pressure in the inlet line). During the compression of the gas in the compression chamber (the pressure in the compression chamber is higher than the pressure in the inlet line), the inlet valve closes the compression chamber off from the inlet line.

Arranged between the compression chamber and the outlet line is an outlet valve, which is open during the ejection of the compressed gas from the compression chamber (the pressure in the compression chamber is higher than the pressure in the outlet line) and in this way defines a connection between the compression chamber and the outlet line. While gas to be compressed is being drawn into the compression chamber, the outlet valve closes off the connection between the compression chamber and outlet line (the pressure in the compression chamber is lower than the pressure in the outlet line), in order to prevent compressed gas from flowing back into the compression chamber from the outlet line.

Both for inlet valves and for outlet valves of piston compressors, use is frequently made of valves having a closing body which, depending on the pressure difference on the two sides of the valve, is pressed onto the valve seat and as a result closes, or is lifted from the valve seat, with the result that the valve opens. A conventional design of such valves has a valve tongue that serves as a closing body.

The piston compressor according to the invention has a venting device, through which compressed gas is able to be discharged from the compression chamber in order to lower the pressure therein. In this case, in particular compressed gas is able to be discharged, which passes back into the compression chamber from the pressurized outlet line during separation of the piston compressor from the drive device in particular on account of an outlet valve not closing fully and causes a pressure increase therein.

In one embodiment of the piston compressor, the compressed gas is able to be discharged from the compression chamber into a region at lower pressure, in particular ambient pressure, by means of the venting device. In this way, the compressed gas can escape into a region which exhibits a lower pressure than the compression chamber, into which compressed gas has penetrated from the outlet line. As a result of the compressed gas being discharged, the pressure in the compression chamber drops.

In one embodiment of the piston compressor, the region at ambient pressure is formed by the environment itself, a gas chamber connected to the inlet system or the inlet line, or the interior of the crankcase of the piston compressor. A region at ambient pressure in the inlet system can be for example the inlet line or a gas chamber connected thereto, which is formed for example in the cylinder head of the piston compressor and thus also represents a part of the inlet line. In an embodiment in which the region at ambient pressure is formed by the interior of the crankcase of the piston compressor, the gas flowing out of the compression chamber of the piston compressor through the venting device is conveyed into the crankcase, where in particular pressure equalization takes place first in the crankcase and then with the environment via the venting system thereof.

In this case, pressure fluctuations can occur both in a gas chamber connected to the inlet system and in the crankcase of the piston compressor: in the inlet system in particular depending on the intake of fresh gas—for example when the inlet system is connected to the inlet system of a combustion engine of correspondingly large size—or on account in particular of preceding crank drive movements in the crankcase. Since, however, both the inlet system and the crankcase are connected to the environment and constant equalization of pressure fluctuations with the environment usually takes place there, the pressure prevailing in a gas chamber connected to the inlet system or in the crankcase is considered to be ambient pressure in the scope of this invention.

In one embodiment of the piston compressor, a switchable valve device forms the venting device, by means of which compressed gas is able to be discharged from the compression chamber in that a connection of the compression chamber with a region at lower pressure, in particular ambient pressure, is able to be established.

In this case, it can be a switchable valve device by means of which the compression chamber of the piston compressor is optionally connectable to a region at lower pressure, in particular ambient pressure, via a venting opening arranged for example in the valve plate or in the cylinder wall. For this purpose, use can be made in particular of a 2/2-way valve, which is switchable for example such that it opens and closes in particular in parallel with or in an offset manner with respect to the actuation of the clutch and in this way allows pressure equalization in the compression chamber as a result of the discharging of compressed gas, as long as the piston compressor is not being driven. However, provision can also be made to also switch such a valve device in a manner depending on other parameters, for example the pressure actually prevailing in the compression chamber, this pressure being sensed via pressure sensors connected thereto or in some other suitable manner.

Another embodiment of the piston compressor has an unblockable check valve, which also acts as the inlet valve. Such an unblockable check valve represents a switchable valve device which is arranged between the inlet line and the compression chamber of the compressor and opens and closes the connection between the inlet line and compression chamber in particular automatically in accordance with the function of an inlet valve. In addition, such an unblockable check valve represents a switchable valve device by means of which the connection between the inlet line and compression chamber is optionally openable and closable in order to allow pressure to be broken down by compressed gas being discharged from the compression chamber.

For example, such an unblockable check valve, just like the above-described switching valve, is switchable in parallel with or in a manner offset with respect to the clutch actuation or in dependence on other parameters, connected in particular with the pressure in the compression chamber, which are sensed for example by means of sensors. By way of the inlet valve in the form of an unblockable check valve being opened while the compressor is inoperative, pressure equalization between the compression chamber and the inlet system can take place, such that no significant buildup of pressure can take place in the compression chamber.

In a further embodiment of the piston compressor, a check valve forms the venting device, by means of which compressed gas is able to be discharged from the compression chamber. Such a check valve is designed in particular such that it opens and connects the compression chamber to a region at lower pressure, in particular ambient pressure, when the pressure in the compression chamber rises during a first compression stroke, on account of a compressed gas having passed back into the compression chamber from the outlet line during separation of the piston compressor from the drive device, to such an extent that there is a risk of damage to the piston compressor or to a device connected to the piston compressor. In this case, the check valve establishes a connection of the compression chamber to a region at lower pressure, in particular ambient pressure, with the result that the compressed gas, which has passed back into the compression chamber from the outlet line during separation of the piston compressor from the drive device, is able to be discharged. As a result, the pressure in the compression chamber does not rise above a maximum value defined by the check valve during the first compression stroke of the piston compressor after the closing of the clutch, in spite of an increased pressure in the compression chamber caused by a compressed gas having penetrated into the latter.

In a further embodiment, the inlet valve forms the venting device. In this case, the inlet valve is configured such that a connection between the inlet line and the compression chamber is closable thereby only from a pressure in the compression chamber which is at least 0.1 bar, preferably at least 0.2 bar and in particular at least 0.5 bar higher than the pressure in the inlet line, said pressure corresponding substantially to ambient pressure. In this case, at a pressure in the compression chamber that is below the limit value of at least 0.1 bar, preferably at least 0.2 bar and in particular at least 0.5 bar of overpressure, there is a continuous connection between the inlet line and the compression chamber. In this way, a compressed gas that passes into the compression chamber during separation of the piston compressor from the drive device, i.e. when the piston compressor is inoperative, is able to be discharged into the inlet line as a result of this opening of the inlet valve, without pressure building up in the compression chamber of the compressor.

In one embodiment of the piston compressor, in which the inlet valve is closable only from a predetermined pressure in the compression chamber, the inlet valve has a valve seat formed in a concave manner in particular on the valve plate and a valve tongue formed in a substantially planar manner such that the valve tongue bears in a sealing manner against the valve seat only after an elastic deformation brought about by a pressure in the compression chamber. In such an embodiment, the inlet valve closes only when a sufficiently high pressure acts in the compression chamber during the compression stroke, said pressure deforming the valve tongue such that the latter bears in a sealing manner against the valve seat formed in a concave manner. As long as the pressure in the compression chamber has a lower value than the pressure which results in the inlet valve closing, the inlet valve is open. Thus, no pressure buildup in the compression chamber can be brought about by compressed gas which passes back into the compression chamber from the outlet line during the separation of the piston compressor from the drive device.

In another embodiment of the piston compressor, in which the inlet valve is closable only from a predetermined pressure in the compression chamber, the inlet valve has a valve seat formed in a planar manner and a valve tongue formed in a curved manner. Consequently, the valve tongue bears in a sealing manner against the valve seat only after an elastic deformation brought about by the pressure in the compression chamber. In this embodiment, too, the inlet valve closes only when a sufficiently high pressure acts in the compression chamber during a compression stroke, said pressure deforming the valve tongue formed in a curved manner such that the latter bears in a sealing manner against the valve seat formed in a planar manner. Here too, the inlet valve remains open as long as the pressure in the compression chamber has a lower value than the pressure which results in the inlet valve closing in particular during a compression stroke. Thus, it is also possible in this embodiment for a compressed gas which passes back into the compression chamber from the outlet line during the separation of the piston compressor from the drive device to result in no pressure buildup in the compression chamber.

In another embodiment of the piston compressor, a venting duct forms the venting device. Through such a venting duct, which establishes in particular a permanent connection to a region at a lower pressure than the compression chamber, in particular ambient pressure, gas can be discharged from one end of the venting duct in the compression chamber, which is at a higher pressure, through the venting duct into a region at lower pressure, in particular ambient pressure, at the other end of the venting duct. As a result, pressure equalization with the compression chamber takes place. Thus, as long as gas passes back into the compression chamber from the pressurized outlet line during separation of the piston compressor from the drive device, an increased pressure cannot build up there, since the gas is discharged through the venting duct.

In one embodiment, at least one end of the venting duct is arranged in the valve plate and establishes in particular a connection of the compression chamber to the environment of the piston compressor or to the inlet system thereof. A drawback of a permanently open venting duct is that the latter allows gas to escape from the compression chamber even during a compression stroke, thereby reducing the efficiency of the compressor. In one embodiment, however, the venting duct has such a small cross section that pressure equalization through the venting duct is possible, but the throttle action of the small cross section of the venting duct prevents the pressure flow of a larger volume flow during a compression stroke.

An alternative design, which limits gas escaping from the compression chamber during a compression stroke, has a suitable shut-off valve in the venting duct, said shut-off valve closing the latter from a predetermined overpressure. A suitable shut-off valve for this purpose is for example a gravity ball valve. Advantageously, such a shut-off valve is embodied to be robust with respect to soiling by lubricating oil contaminants.

In another embodiment, at least one end of the venting duct is arranged in the cylinder wall, said duct establishing for example a connection with the environment of the piston compressor. Starting from the outer side of the cylinder wall, the venting duct can have a connecting device in the form of a line, which serves as an extension of the venting duct and connects the latter in particular to the inlet system or to the interior of the crankcase of the piston compressor. Such a venting duct, too, forms an opening in the compression chamber, through which it is also possible for gas to escape from the compression chamber during the compression stroke, thereby reducing the efficiency of the piston compressor. Therefore, the venting duct is designed in particular to be large enough to ensure pressure equalization in order that the gas volume flow which can be discharged from the compression chamber therethrough during separation of the compressor from the drive device is at least as large as the gas volume flow of compressed gas from the outlet line that has passed back into the compression chamber from the outlet line in this period of time.

In one embodiment, the venting duct is arranged in the cylinder wall such that one end is passed by the piston from a particular piston position during the compression stroke and is thus closed. This is in particular the case when the venting duct is arranged between a central stroke position of the piston and top dead center thereof. As a result of this arrangement of the venting duct, a gas that has passed back into the compression chamber from the outlet duct while the piston compressor is inoperative is able to be discharged in order to prevent pressure buildup in the compression chamber. At the same time gas is prevented from escaping from the compression chamber as soon as a piston ring has passed the opening of the venting duct during the movement toward top dead center.

In one embodiment of the piston compressor, a check valve or a shut-off valve is arranged in the venting duct or in a connecting device connected thereto. Such a check valve or shut-off valve can prevent gas escaping from the compression chamber during a compression stroke of the piston compressor, and such a check valve or shut-off valve can also serve to prevent possibly contaminated gas from being drawn in particular from the crankcase into the compression chamber.

Although, in the above text, the piston, the cylinder, the cylinder head etc. have been addressed in each case in connection with the components of the piston compressor, the properties described with regard thereto also each apply to a piston compressor having two or more of these elements, since the present invention can be used not only for single-stage piston compressors but also for multistage piston compressors.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an example of a prior art piston compressor.

FIG. 2 is an illustration of an example of an outlet valve as is used in piston compressors in the prior art.

FIG. 3 is a schematic illustration of a first exemplary embodiment of a piston compressor according to the invention, in which the venting device has a switchable valve device.

FIG. 4 is a schematic illustration of a second exemplary embodiment of a piston compressor according to the invention, in which the venting device has a switchable valve device.

FIG. 5 is a schematic illustration of a third exemplary embodiment of a piston compressor according to the invention, in which the venting device has a check valve.

FIG. 6 is a schematic illustration of a fourth exemplary embodiment of a piston compressor according to the invention, in which the venting device has a venting duct.

FIG. 7 is a schematic illustration of a fifth exemplary embodiment of a piston compressor according to the invention, in which the venting device has a venting duct with a shut-off valve.

FIG. 8 is a schematic illustration of a sixth exemplary embodiment of a piston compressor according to the invention, in which the venting device has a venting duct.

FIG. 9 is a schematic illustration of a seventh exemplary embodiment of a piston compressor according to the invention, in which the venting device has a venting duct.

FIG. 10 is a schematic illustration of an eighth exemplary embodiment of a piston compressor according to the invention, in which the venting device has a venting duct.

FIG. 11 is an illustration of a detail of a ninth exemplary embodiment of a piston compressor according to the invention, in which the inlet valve forms the venting device.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of an example of a piston compressor 10 as is known from the prior art. The crankshaft 11 of the piston compressor 10 is connected to a drive device (not illustrated, in this case a combustion engine) via a clutch 3 and is separable selectively from this drive device by way of the clutch 3. Therefore, with the clutch 3 open, no torque is transmitted to the crankshaft 11 of the piston compressor 10, and so the crankshaft 11 is stationary during the separation of the piston compressor 10 from the drive device.

The crankshaft 11 is connected to a connecting rod 12, mounted eccentrically thereon, on which a piston 13 is mounted. The piston 13 is mounted in an axially movable manner in a cylinder 14 of the piston compressor 10. The crank drive 15 having at least one crankshaft 11, one connecting rod 12 and one piston 13 is arranged in a crankcase 16 which is firmly connected to the cylinder 14. As a result of a rotary movement of the crankshaft 11, the piston 13 is moved in the cylinder 14 by the connecting rod 12 such that it executes a stroke movement.

Above the piston 13, the cylinder 14 is closed by a valve plate 20. Thus, the cylinder 14, the piston 13 and the valve plate 20 define the compression chamber 17 in the cylinder 14. Arranged on the valve plate 20 is an inlet valve 21, which is arranged between an inlet line 22 and the compression chamber 17. The inlet line 22 is part of an inlet system 23 which draws in fresh air from the environment through a filter (not illustrated) and feeds it to the compression chamber 17 via the inlet line 22 through the cylinder head (not illustrated). The cylinder head is arranged above the valve plate 20 and has a cylinder-head volume 24 which is connected to the compression chamber 17 via the inlet valve 21. The inlet valve 21 is embodied in this case as a shut-off valve, which allows fresh air to be drawn into the compression chamber 17 but prevents the air drawn into the compression chamber 17 via the inlet line 22 from flowing back.

Also arranged on the valve plate 20 is an outlet valve 26, which is arranged between the compression chamber 17 and an outlet line 27. Via the outlet line 27, compressed gas, in this case air, is fed to a compressed-air reservoir (not illustrated here). In this case, the outlet valve 26, which is likewise embodied as a shut-off valve, prevents compressed air from flowing back into the compression chamber 17 from the outlet line 27.

FIG. 2 shows an illustration of an example of an outlet valve 26 as is frequently used in piston compressors 10 in the prior art. The outlet valve 26 is arranged on the valve plate 20 of the piston compressor 10 above the compression chamber 17. The valve plate 20 has an outlet opening 28, which connects the compression chamber 17 to a cylinder-head volume 27 a arranged in the valve plate 20 and cylinder head of the piston compressor 10, said cylinder-head volume 27 a forming part of the outlet line 27.

The outlet valve 26 has, as valve body, a valve tongue 26 a, which detaches from the valve seat 26 b from a predetermined pressure difference between the compression chamber 17 and the outlet line 27 and allows air to flow through from the compression chamber 17 into the outlet line 27. The outlet valve 26 also has an abutment element 26 c, arranged above the outlet opening 28, against which the valve tongue 26 a bears in the open state. As soon as the valve tongue 26 a detaches from the valve seat 26 b, the pressurized air can flow out of the compression chamber 17, through the lateral open regions past the valve tongue 26 a and the abutment element 26 c, and into the outlet line 27.

If contaminants from the compression chamber 17 or from the cylinder-head volume 27 a, which are detached for example by deposits formed by residues in the air flowing through from the hot top side of the piston 13, from the valve plate 20 or from the cylinder-head volume 27 a, pass between the valve tongue 26 a and the valve seat 26 b, there is a risk of the outlet valve 26 no longer closing fully. In this case, compressed air can flow back into the compression chamber 17 from the outlet line 27 as soon as the pressure in the compression chamber 17 drops below the pressure in the outlet line 27. In the case of a 12.5-bar compressed-air system of a commercial vehicle, the compression chamber 17 of the piston compressor 10 can be subjected to a pressure of up to 6 bar for example by the air flowing back thereto. If the piston compressor 10 is then connected to the drive device again, the piston compressor 10 generates an internal pressure of about 60 bar during the first stroke. If the compression chamber 17 withstands this enormous internal pressure, the resultant torque at the crankshaft 11 is usually much too high for the clutch 3 and so the latter slips, overheats and wears inadmissibly quickly.

FIG. 3 shows a schematic illustration of a first exemplary embodiment of a piston compressor 10 according to the invention. The structure of the piston compressor 10 in FIG. 3 corresponds largely to the structure of the piston compressor 10 illustrated in FIG. 1 and described in that regard, and so identical elements of the piston compressors 10 are denoted by identical reference signs. In the following text, only the differences of the piston compressor 10 in FIG. 3 from the piston compressor 10 in FIG. 1 are explained.

The piston compressor 10 illustrated in FIG. 3 has a venting device in the form of a 2/2-way valve 31, which is arranged between the compression chamber 17 and the inlet system 23. The 2/2-way valve is a switchable valve device. In the exemplary embodiment in FIG. 3, the control line 31 a of the 2/2-way valve 31 is connected in terms of signaling to the controller of the clutch 3. If the clutch 3 is opened and the piston compressor 10 is thus no longer driven, the 2/2-way valve 31 is switched from the illustrated closed position into an open position in order to establish a connection, through which air is able to flow, between the compression chamber 17 and the inlet system 23.

If, while the piston compressor 10 is inoperative, for example in the case of an outlet valve 26 that no longer closes in a leaktight manner, compressed air now passes into the compression chamber 17, it is possible for pressure equalization with the inlet line 22 to take place by way of the open 2/2-way valve 31. Thus, no pressure buildup can take place in the compression chamber 17, which could result in damage to the piston compressor 10 and/or the clutch 3, in particular during the first compression stroke of the piston compressor 10 when the latter is restarted.

FIG. 4 shows a schematic illustration of a second exemplary embodiment of a piston compressor 10 according to the invention. The structure of the piston compressor 10 in FIG. 4 also corresponds largely to the structure of the piston compressor 10 illustrated in FIG. 1 and described in that regard, and so identical elements of the piston compressors 10 are denoted by identical reference signs. In the following text, only the differences of the piston compressor 10 in FIG. 4 from the piston compressor 10 in FIG. 1 are explained.

The piston compressor 10 illustrated in FIG. 4 has a venting device in the form of an unblockable check valve 32, which also serves at the same time as an inlet valve. Thus, the unblockable check valve 32 is arranged between the compression chamber 17 and the inlet system 23. While fresh air is being drawn into the compression chamber 17 from the inlet line 22, the unblockable check valve 32 opens automatically on account of the pressure difference prevailing there. The unblockable check valve 32 is also a switchable valve device, which, in addition to automatically opening when drawing in fresh air, is also switchable into an open position by means of a control signal. In the exemplary embodiment in FIG. 4, the control line 32 a of the unblockable check valve 32 is connected in terms of signaling to a control device (not illustrated). Depending on at least one predetermined parameter, for example the pressure in the compression chamber 17, it is thus possible for the unblockable check valve 32 to be opened in order to establish a connection between the compression chamber 17 and the inlet line 22.

If, while the piston compressor 10 is inoperative, for example in the case of an outlet valve 26 that no longer closes in a leaktight manner, compressed air now passes into the compression chamber 17, the unblockable check valve 32 can be opened in order to allow pressure equalization with the inlet line 22. Thus, no pressure buildup can take place in the compression chamber 17, which could result in damage to the piston compressor 10 and/or the clutch 3, in particular during the first compression stroke of the piston compressor 10 when the latter is restarted.

When the piston compressor 10 is started again, the unblockable check valve 32 is switched by the control device back into the working position, in which it automatically opens, while fresh air is being drawn into the compression chamber 17 from the inlet line 22, on account of the pressure difference prevailing there.

FIG. 5 shows a schematic illustration of a third exemplary embodiment of a piston compressor 10 according to the invention. The structure of the piston compressor 10 in FIG. 5 also corresponds largely to the structure of the piston compressor 10 illustrated in FIG. 1 and described in that regard, and so identical elements of the piston compressors 10 are denoted by identical reference signs. In the following text, only the differences of the piston compressor 10 in FIG. 5 from the piston compressor 10 in FIG. 1 are explained.

The piston compressor 10 illustrated in FIG. 5 has a venting device in the form of a check valve 33, which is arranged between the compression chamber 17 and the inlet system 23. The check valve 33 arranged in addition to the inlet valve 21 between the compression chamber 17 and the inlet system 23 blocks in the opposite direction to the inlet valve 21, and so it is closed while fresh air is being drawn into the compression chamber 17 and during compression of the piston compressor 10 in normal operation.

If, in the embodiment shown in FIG. 5, while the piston compressor 10 is inoperative, for example in the case of an outlet valve 26 that no longer closes in a leaktight manner, compressed air passes into the compression chamber 17, first of all a pressure buildup in the compression chamber 17 takes place here. The pressure that is established in the process does not reach a higher value than during a compression stroke, and so initially no venting of the compression chamber 17 is necessary. It is only during the first compression stroke of the piston compressor 10 after it has been restarted that a much higher pressure arises on account of the precompressed air in the compression chamber 17, it being possible for this much higher pressure to result in damage to the piston compressor 10 and/or clutch 3. Therefore, the check valve 33 is designed such that it opens a connection between the compression chamber 17 and the inlet line 21 with a sufficiently large cross section in order to discharge air from the compression chamber 17 as soon as the pressure in the compression chamber 17 exceeds a critical value. In the exemplary piston compressor 10 for a commercial vehicle, the peak pressure in the compression chamber during normal operation is between about 16 and 19 bar. An exemplary check valve 33 is therefore embodied such that it opens for example at a pressure of 20 bar in the compression chamber 17 and thus discharges compressed air out of the compression chamber 17.

FIG. 6 shows a schematic illustration of a fourth exemplary embodiment of a piston compressor 10 according to the invention. The structure of the piston compressor 10 in FIG. 6 also corresponds largely to the structure of the piston compressor 10 illustrated in FIG. 1 and described in that regard, and so identical elements of the piston compressors 10 are denoted by identical reference signs. In the following text, only the differences of the piston compressor 10 in FIG. 6 from the piston compressor 10 in FIG. 1 are explained.

The piston compressor 10 illustrated in FIG. 6 has a venting device in the form of a venting duct 34, which is arranged between the compression chamber 17 and the inlet system 23. The venting duct 34 establishes a connection, through which air is able to flow, between the compression chamber 17 and the inlet system 23, such that, while the piston compressor is inoperative, a pressure which is significantly greater than ambient pressure cannot build up in the compression chamber 17.

In the embodiment shown in FIG. 6, the venting duct 34 is arranged in the region of the valve plate 20 on the top side of the cylinder 14, such that, by way of the venting duct 34, continuous pressure equalization with the inlet line 32 of the piston compressor 10 takes place. If, while the piston compressor 10 is inoperative, compressed air passes into the compression chamber 17 from the outlet line 27, pressure equalization with the inlet line 22 takes place by way of the venting duct 34, with the result that a pressure buildup in the compression chamber 17 cannot occur. A drawback of such a venting duct 34, however, is that it is also open during a compression stroke of the piston compressor 10 and air to be compressed in this phase escapes from the compression chamber 17. This reduces the efficiency of the piston compressor 10. The venting duct 34 is therefore designed such that it has only a small cross section in order to allow sufficient pressure equalization with the inlet system 23 while the piston compressor 10 is inoperative, but has a throttle action at high pressures in order to limit the volume flow of the discharged air.

FIG. 7 shows a schematic illustration of a sixth exemplary embodiment of a piston compressor 10 according to the invention. The structure of the piston compressor 10 in FIG. 7 corresponds largely to the structure of the piston compressor 10 illustrated in FIG. 6 and described in that regard, and so identical elements of the piston compressors 10 are denoted by identical reference signs. In the following text, only the differences of the piston compressor 10 in FIG. 7 from the piston compressor 10 in FIG. 6 are explained.

FIG. 7 shows a piston compressor 10 which has also a venting device in the form of a venting duct 39, which is arranged between the compression chamber 17 and the inlet system 23. Arranged in the venting duct 39 is a shut-off valve in the form of a gravity ball valve 40, which closes the venting duct 39 when the pressure in the compression chamber 17 exceeds a predetermined value which pushes the ball of the gravity ball valve 40 counter to the gravitational force thereof against a valve seat arranged above in the gravity ball valve 40. By way of the shut-off valve, any escape of compressed air from the compression chamber 17 during a compression stroke is limited.

FIG. 8 shows a schematic illustration of a sixth exemplary embodiment of a piston compressor 10 according to the invention. The structure of the piston compressor 10 in FIG. 8 corresponds largely to the structure of the piston compressor 10 illustrated in FIG. 6 and described in that regard, and so identical elements of the piston compressors 10 are denoted by identical reference signs. In the following text, only the differences of the piston compressor 10 in FIG. 8 from the piston compressor 10 in FIG. 6 are explained.

The piston compressor 10 illustrated in FIG. 8 also has a venting device in the form of a venting duct 35, which is arranged between the compression chamber 17 and the inlet system 23. In contrast to the piston compressor 10 in FIG. 6, the venting duct 35 is arranged in the upper region of the wall of the cylinder 14. The venting duct 35 also establishes a connection, through which air is able to flow, between the compression chamber 17 and the cylinder-head volume 24, which allows pressure equalization between the compression chamber 17 and the inlet system 23.

As is shown in FIG. 8, the venting duct 35 can be arranged approximately in the region swept by the upper piston ring approximately 60° before top dead center of the piston 13. As a result, while the piston compressor 10 is inoperative, compressed air is discharged from the compression chamber 17, said air passing thereto from the outlet line 27 while the piston compressor 10 is separated from the drive device. At the same time, however, the air in the compression chamber 17 is prevented from escaping therefrom during the end phase of the compression stroke.

FIG. 9 shows a schematic illustration of a seventh exemplary embodiment of a piston compressor 10 according to the invention. The structure of the piston compressor 10 in FIG. 9 corresponds largely to the structure of the piston compressor 10 illustrated in FIG. 8 and described in that regard, and so identical elements of the piston compressors 10 are denoted by identical reference signs. In the following text, only the differences of the piston compressor 10 in FIG. 9 from the piston compressor 10 in FIG. 8 are explained.

The piston compressor 10 illustrated in FIG. 9 has a venting device in the form of a venting duct 36, which is arranged between the compression chamber 17 and the interior of the crankcase 16. As in the case of the piston compressor 10 in FIG. 8, the venting duct 36 is arranged in the upper region of the wall of the cylinder 14. It establishes a connection, through which air is able to flow, between the compression chamber 17 and the crankcase 16. Since the crankcase 16 of the piston compressor 10 allows pressure equalization with respect to the environment, essentially ambient pressure prevails in the interior thereof. Thus, pressure equalization between the compression chamber 17 and the crankcase 16 can take place via the venting duct 36.

FIG. 10 shows a schematic illustration of an eighth exemplary embodiment of a piston compressor 10 according to the invention. The structure of the piston compressor 10 in FIG. 10 corresponds largely to the structure of the piston compressor 10 illustrated in FIG. 9 and described in that regard, and so identical elements of the piston compressors 10 are denoted by identical reference signs. In the following text, only the differences of the piston compressor 10 in FIG. 10 from the piston compressor 10 in FIG. 9 are explained.

The piston compressor 10 illustrated in FIG. 10 has a venting device in the form of a venting duct 37, which, in a manner corresponding to the venting duct 36 in FIG. 9, is arranged between the compression chamber 17 and the interior of the crankcase 16. Compared with the venting duct 36 in FIG. 9, a check valve 38 is arranged in the venting duct 37, said check valve 38 preventing air from flowing back into the compression chamber 17 from the crankcase 16. The check valve 38 can in this case be designed such that, even at a small pressure difference between the pressure in the compression chamber 17 and the pressure in the crankcase 16, it opens in order to prevent a pressure buildup in the compression chamber 17 during a down time of the piston compressor 10.

FIG. 11 shows an illustration of a detail of a ninth exemplary embodiment of a piston compressor 10 according to the invention, in which the inlet valve 21 forms the venting device. The elements of the inlet valve 21 are shown in an exploded illustration in FIG. 11. The inlet valve 21 forms the upper termination of the compression chamber 17 in the cylinder 14. The valve tongue 21 a is embodied in one piece with a first element of the inlet valve 21, which is arranged between the cylinder 14 and an abutment element 21 b of the inlet valve 21. The abutment element 21 b, illustrated by way of example, has two valve openings 21 c, which, depending on the pressure difference between the compression chamber 17 in the cylinder 14 and the pressure in the inlet system 23, are closed by the valve tongue 21 a.

The valve tongue 21 a has a curvature, which is designed such that the valve tongue 21 a bears against the abutment element 21 b (dashed illustration of the valve tongue 21 a) from a pressure in the compression chamber 22 which is 0.4 bar higher than the pressure in the inlet system 23 (ambient pressure) in the exemplary embodiment and in this case closes the valve openings 21 c. At a pressure difference of less than 0.4 bar, the valve tongue 21 a always has a curvature, and so there is a connection between the inlet system 23 and the compression chamber 17. Thus, a compressed gas which has passed into the compression chamber 17 is able to be discharged through the valve openings 21 c of the inlet valve 21 into the inlet line 22 without a pressure buildup in the compression chamber 17 of the compressor 10 occurring.

In another embodiment of the piston compressor 10 which is not shown but acts in the same way, the inlet valve 21 can also have an abutment element 21 b which has a recess in the region of the valve openings 21 c, such that the valve tongue 21 a bears in a sealing manner against the abutment element 21 b only from a predetermined pressure in the compression chamber 17 in this embodiment, too.

LIST OF REFERENCE SIGNS

-   3 Clutch -   10 Piston compressor -   11 Crankshaft -   12 Connecting rod -   13 Piston -   14 Cylinder -   15 Crank drive -   16 Crankcase -   17 Compression chamber -   20 Valve plate -   21 Inlet valve -   21 a Valve tongue -   21 b Abutment element -   21 c Valve opening -   22 Inlet line -   23 Inlet system -   24 Cylinder-head volume (inlet) -   26 Outlet valve -   26 a Valve tongue -   26 b Valve seat -   26 c Abutment element -   27 Outlet line -   27 a Cylinder-head volume (outlet) -   28 Outlet opening -   31 2/2-Way valve -   31 a Control line -   32 Check valve -   32 a Control line -   33 Check valve -   34 Venting duct -   35 Venting duct -   36 Venting duct -   37 Venting duct -   38 Check valve -   39 Check valve -   40 Gravity ball valve

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

What is claimed is:
 1. A piston compressor for compressing a gas, which compression is optionally separable from a drive device by way of a clutch, comprising: an inlet valve, which is arranged between an inlet line for the gas to be compressed and a compression chamber of the piston compressor; an outlet valve, which is arranged between the compression chamber of the piston compressor and an outlet line for compressed gas; and a venting device, through which compressed gas, which passes from the outlet line back into the compression chamber during a separation of the piston compressor from the drive device, is able to be discharged from the compression chamber.
 2. The piston compressor as claimed in claim 1, wherein the compressed gas is able to be discharged from the compression chamber into a region at ambient pressure, which is formed by an environment itself, a gas chamber connected to an inlet system, or an interior of the crankcase.
 3. The piston compressor as claimed in claim 1, wherein a switchable valve device forms the venting device.
 4. The piston compressor as claimed in claim 1, wherein a check valve forms the venting device.
 5. The piston compressor as claimed in claim 1, wherein the inlet valve forms the venting device, the inlet valve is configured such that a connection between the inlet line and the compression chamber is closable thereby only from a predetermined pressure in the compression chamber, and the predetermined pressure is at least 0.1 bar higher than the pressure in the inlet line.
 6. The piston compressor as claimed in claim 5, wherein the predetermined pressure is at least 0.2 bar higher than the pressure in the inlet line.
 7. The piston compressor as claim in claim 5, wherein the predetermined pressure is at least 0.5 bar higher than the pressure in the inlet line.
 8. The piston compressor as claimed in claim 5, wherein the inlet valve has a valve seat formed in a concave manner and a valve tongue formed in a substantially planar manner such that the valve tongue bears in a sealing manner against the valve seat only after an elastic deformation brought about by the pressure in the compression chamber.
 9. The piston compressor as claimed in claim 5, wherein the inlet valve has a valve seat formed in a planar manner and a valve tongue formed in a curved manner, such that the valve tongue bears in a sealing manner against the valve seat only after an elastic deformation brought about by the pressure in the compression chamber.
 10. The piston compressor as claimed in claim 1, wherein a venting duct forms the venting device.
 11. The piston compressor as claimed in claim 10, wherein at least one end of the venting duct is arranged in a valve plate or in a cylinder wall.
 12. The piston compressor as claimed in claim 10, wherein a check valve or a shut-off valve is arranged in the venting duct.
 13. The piston compressor as claimed in claim 11, wherein a check valve or a shut-off valve is arranged in the venting duct. 